1. Field of the Invention
The present invention relates to suspension systems for motor vehicles. More specifically, the present invention relates to a suspension system for a steerable wheel which increases adjustability of performance characteristics.
2. Disclosure Information
In a conventional suspension system for a motor vehicle having a steerable wheel and tire assembly, the wheel is rotatably supported on a spindle which extends from a knuckle. Typically an upper and a lower control arm pivotally interconnect the knuckle to a chassis. A single ball joint pivotally connects the upper arm to the upper portion of the knuckle and a single ball joint pivotally connects the lower arm to the lower portion of the knuckle. This configuration allows both steerable motion of the wheel in the horizontal plane of the vehicle, and jounce and rebound motion in the vertical plane of the vehicle.
In such a suspension system, a line extending from the upper ball joint to the lower ball joint defines a "kingpin" axis. Orientation of the kingpin axis defines certain operational characteristics of the suspension. In designing a suspension system as described above, the placement of the kingpin axis is limited by the package space available for the arms. Space for the upper and lower arms must be shared with other components, including the engine, brake hardware, spring and shock absorber assembly, and supporting chassis structure.
One solution providing greater design flexibility for locating the kingpin axis is shown in U.S. Pat. No. 4,878,688. This patent discloses a suspension system providing an upper pair of lateral links and a lower pair of lateral links. Each link attaches to the knuckle with a separate ball joint. Utilizing ball joints this way creates an instant center of velocity located at the intersection of coaxial lines extended along the longitudinal axis of each of the independent links. The instant center is an imaginary point that does not have physical package constraints, thereby obviating to some extent the packaging restrictions imposed by neighboring componentry. The kingpin axis for such a system is defined by connecting a straight line through the instant centers. This flexibility does allow designers to orient the kingpin axis to pass througth the center of the wheel, thereby providing zero kingpin offset, and still provides a negative scrub radius at the contact patch. While this system does allow the kingpin axis to be defined where packaging space otherwise would not allow it, the system presents several objectionable characteristics. First, the system is costly. Each ball joint used adds significantly to the cost of the suspension. Second, steering system sensitivity to undesirable force variations is increased. Third, the kingpin orientation is overly susceptible to manufacturing tolerance variations in both the upper arm to chassis mounts, and to the upper arm construction and installation.
It would be desirable to have a suspension system that would allow greater flexibility for orienting the kingpin axis that simultaneously overcomes the deficiency of the prior art. Specifically, it would be desirable to provide an uncomplicated, low cost, lightweight suspension while reducing the sensitivity of the steering system to undesirable vibrations.